The present invention relates to a modulator and a modulation method for use, in particular but not exclusively, in cellular telecommunication networks.
In the various known cellular telecommunication networks, modulation is required in order to transmit data in the frequency band which has been allocated to the base station or mobile station in the particular cellular network. The frequencies which are typically used in cellular telecommunication networks for communication between base stations and mobile stations are relatively high frequencies which are much greater than those frequencies with which current digital technology can deal. Accordingly, digital circuitry of a cellular telecommunication network will use a base band frequency, which is much lower than the frequency used to transmit data between, for example base stations and mobile stations. After processing by the base station or mobile station, the data will be modulated onto the carrier frequency to be used.
A large number of different modulation methods are known but these modulation methods can be generally divided up into three categories. The first category uses amplitude modulation, the second category uses phase modulation whilst the third uses frequency modulation. Modulation methods which use a combination of these three known categories are known. For example quadrature amplitude modulation is a combination of amplitude and phase modulation. In the GSM standard for wireless communication, Gaussian Minimum Shift Keying (GMSK) is used which is a form of frequency modulation. However, the modulators which are currently used are generally only able to support a single modulation method. In other words, each modulator is specifically designed for a single modulation method. Thus, for every different type of modulation method used in cellular telecommunication networks, a separate modulator needs to be provided. This is disadvantageous in that a number of different modulators may need to be stocked by a manufacturer of mobile and base stations. Another problem is that it is also difficult to modify existing base and mobile stations to introduce new modulation methods. This may increase the time required in order to introduce new standards or alternatively may deter network operators from changing the modulation method used even if the new modulation method is more efficient. Additionally, during the design of new cellular network standards, it is often uncertain as to what modulation method will ultimately be used. This can increase the length of time required in order to get equipment such as base transceiver stations and mobile stations incorporating the required modulator onto the market.
According to one aspect of the present invention, there is provided a modulator for modulating input data, said modulator comprising an input for receiving data to be modulated; a plurality of memory regions arranged to contain information relating to a modulation method to be carried out by said modulator, at least one of said memory regions providing time independent modulation values and at least one of said memory regions providing time dependent modulation values, the values provided by said memory regions being dependent on the data received via said input; and processing means for providing a modulating signal based on the values provided by said memory regions.
It should be appreciated, that the above defined modulator incorporates a new manner of achieving modulation, that is having a plurality of memory regions, at least one of which provides time independent values and at least one of which provides a time dependent modulation value. This may be advantageous in achieving modulation relatively simply for otherwise quite complex modulation methods.
According to a second aspect of the present invention, there is provided a modulator for modulating input data, said modulator comprising an input for receiving data to be modulated; a plurality of memory regions arranged to contain information relating to a modulation method to be carried out by said modulator, at least one of said memory regions providing amplitude modulation values and at least one of the memory regions providing phase modulation values, the values provided by said memory regions being dependent on the data received via said input; and processing means for providing a modulation signal based on the values provided by said memory region.
In this modulator, the memory regions provide phase modulation and amplitude modulation values. Again this allows quite complex modulation methods to be implemented quite simply.
Preferably, the memory regions comprise a memory region arranged to provide time independent phase modulation values and a memory region arranged to provide time dependent phase modulation values. It should be appreciated that with this modulator, it is possible to support virtually all modulation methods which employ phase and frequency.
Preferably, the memory regions comprise a memory region arranged to provide time dependent amplitude modulation values and a memory region arranged to provide time independent amplitude modulation values. Again, these two memory regions allow any type of amplitude modulation to be supported.
In the second aspect of the invention, preferably said at least one of said memory regions providing amplitude modulation values provide at least one of the following values: time independent amplitude modulation values and time dependent amplitude modulation values. Preferably, said at least one of said memory regions providing phase modulation values provide at least one of the following values: time independent phase modulation values and time dependent phase modulation values. A separate memory region is preferably provided for each of the different types of modulation values provided.
The modulator may be arranged to be capable of supporting a plurality of different modulation methods, said memory regions being arranged to contain information relating to the selected modulation method. In this way, the modulator can support a number of different modulation methods and the same modulator can be used in different situations.
The memory regions may be arranged to store values relating to a selected modulation method whereby each memory region provides a look-up table. Alternatively, the memory regions may be arranged to store respective programs from which the values are generated. In this latter situation, a processor may be provided in order to generate the required values from the stored programs or algorithms.
Data control means may be provided, said data control means being arranged to control to which of the memory regions at input data is applied. It should be appreciated that all input data can be applied to all of the memory regions. Alternatively, only some of the input data may be applied to a given memory region. This will depend on the modulation method selected.
Preferably, register means are provided for the memory regions, said register means being arranged to store a predetermined amount of input data. Separate register means may be provided for each of the memory regions. Alternatively at least some of the memory regions may share common register means. Preferably, each value provided by said memory regions is dependent on at least some of the predetermined amount of said input data. By storing the input data in register means, it is possible to take into account the past history of a signal. This is required with some forms of modulation, for example GMSK. The input data may take the form of a series of bits and the register means may be arranged to store a predetermined number of those bits. Those predetermined number of bits of data can be applied, at the same time, to a given memory region in order to obtain the desired output value from the memory region in question.
Means may be provided for combining the outputs from the plurality of the memory regions. These combining means comprise adding means and/or multiplying means, as required by the particular modulation method employed.
A carrier frequency may be combined with the output from one of the memory regions. It should be appreciated that this carrier frequency may be different from that which is used to transmit a signal in a cellular telecommunications network. In particular, the carrier frequency may be much smaller than that used to transmit a signal through an air interface in a cellular telecommunication network.
The output of the or each of the memory regions providing time dependent modulation values may be coupled to respective integrator means. This effectively provides a average for the values over a given period of time. Preferably, the or each memory region arranged to provide time dependent modulation values is arranged to receive a counter signal. This enables a smoother modulation signal to be achieved in that intermediate values can be calculated.
A controller may be provided which provides the information in the memory regions in accordance with the selected modulation method. The amount of input data stored in said register means may be set by a controller. A controller may be arranged to provide information to the data control means indicating to which of the memory regions said input data is to be applied. The provision of a controller which is able to carry out one or more of the above described functions enables the modulator to support a number of different modulation methods including those which require a past history of the input data to be taken into account as well as those which do not. Additionally, the splitting of the data to be applied to the various memory regions can also be controlled in dependence with the selected modulation method. The actual information contained in the memory regions can again be altered as required. The controller may have an external input for providing information relating to the selected modulation method.
Preferably, the outputs of the memory regions providing the time independent and time dependent modulation values are connected to a direct digital synthesiser (DDS) which sums together the outputs of the memory regions. This is particularly advantageous when the DDS is coupled to the memory regions providing phase modulation values. However, the direct digital synthesiser may additionally or alternatively be connected to the or each memory region providing amplitude modulation values. The direct digital synthesiser may receive one input from a memory region providing phase modulation values and one input from a memory region providing amplitude modulation values.
In one preferred embodiment of the present invention, the memory regions comprise four memory regions, one of which provides time independent phase modulation values, the second of which provides time dependent phase modulation values, a third of which provides time dependent amplitude modulation values and the fourth of which provides time independent amplitude modulation values. With these four memory regions, it is possible to provide any known modulation method.
Preferably, the output of the modulator is defined by the following equation:
(∫Axe2x80x2(t,data_amp)dt+Ao(data_amp))cos(xcfx89ct+∫"PHgr"xe2x80x2(t,data_ph)dt+"PHgr"o(data_ph)) xe2x80x83xe2x80x83(1) 
where:
Axe2x80x2 (t,data_amp) is the output of the memory region providing time dependent amplitude modulation values,
Ao (data_amp) is the output of the memory region providing time independent amplitude modulation values,
"PHgr"xe2x80x2 (t,data_ph) is the output of the memory region providing time dependent phase modulation values,
"PHgr"o (data_ph) is the output of the memory region providing time independent phase modulation values, and
xcfx89c is the frequency used to carry the modulation signal.
With this particular equation, it is possible to define any known modulation method and this allows any modulation method to be relatively simply and cheaply implemented.
The modulator may be provided with a plurality of memory regions, wherein in dependence on the selected modulation method, only some of those plurality of memory regions are used. Thus, the number of memory regions used can be selected in accordance with the selected modulation method. The information for the selected modulation method may be provided from an external source to the respective memory region.
Embodiments of the present invention can be incorporated in a station of a cellular telecommunication network. The station may of course be a base station or a mobile telecommunication network.
According to a third aspect of the present invention, there is provided a method of modulating input data comprising the steps of receiving input data to be modulated; providing a plurality of memory regions arranged to contain time independent modulation information and time dependent modulation information; outputting time dependent and time independent modulation values from said respective memory regions in dependence on the received input data; and processing said time dependent modulation values and said time independent modulation values to provide a modulation signal.
According to a fourth aspect of the present invention, there is provided a method of modulating input data comprising the steps of receiving input data to be modulated; providing a plurality of memory regions arranged to contain phase modulation information and amplitude phase modulation information; outputting phase modulation and amplitude modulation values from tsaid respective memory regions in dependence on the received input data; and processing said phase modulation values and said amplitude modulation values to provide a modulation signal.